1. Field of the Invention
The present invention relates to a paper feed cassette that is removably mounted inside an image forming apparatus such as a printer, facsimile machine, or copier of any type. More particularly, the present invention relates to a paper feed cassette provided with a size detection function which permits the detection of paper size and of the presence/absence of the paper feed cassette itself.
2. Description of the Prior Art
An image forming apparatus, irrespective of the type, typically has a paper feed portion provided inside the body thereof, where a paper feed cassette for holding sheets of paper (recording paper) is removably mounted. While paper is being fed from the paper feed cassette to the image forming portion of the image forming apparatus, a formed image is transferred to the paper.
The paper feed cassette is often so structured as to hold paper of different sizes, and therefore, at the stage of image formation, the size of the paper currently loaded therein needs to be recognized precisely so that an image is formed according to the size of the paper fed therefrom.
For this purpose, in many cases, a detecting means is provided that detects the size of the paper loaded in the paper feed cassette when it is mounted in the paper feed portion of the image forming apparatus, and the detection signal from the detecting means is fed to the image forming portion of the image forming apparatus.
For example, Japanese Patent Application Laid-Open No. H5-58465 proposes a recording paper recognition structure as shown in FIGS. 3A to 3C which permits the recognition of three different paper sizes, namely, letter size (with a total length of L1), A4 size (with a total length of L2), and legal size (with a total length of L3), by detecting, with two detection switches S1 and S2 provided in the paper feed portion, the bottom of a guide plate 201 provided integrally with a rear end restricting plate 200 on the paper feed cassette.
Specifically, when the paper feed cassette is mounted inside the image forming apparatus, if the detection switches S1 and S2 are both on, the paper loaded therein is recognized as letter size; if the detection switch S1 is on and the detection switch S2 is off, the paper is recognized as A4 size; if the detection switches S1 and S2 are both off, the paper is recognized as legal size.
In case the user carelessly requests printing without the paper feed cassette mounted in the paper feed portion or in similar situations, it is preferable to inhibit image reading and image formation and warn the user of the absence of the paper feed portion.
To achieve this, the presence/absence of the paper feed cassette (i.e., whether it is mounted or not) needs to be detected. However, in the conventional example (Japanese Patent Application Laid-Open No. H5-58465) described above, the state shown in FIG. 3C, in which legal-size paper is recognized, is identical with the state in which the paper feed cassette is absent. That is, to make it possible to detect also the presence/absence of the paper feed cassette, at least three switches are needed. This increases the number of components and complicates the structure.
An object of the present invention is to provide a paper feed cassette provided with a size detection function which has a simple structure but nevertheless permits the recognition of three or more different image sizes and of the presence/absence of the paper feed cassette.
To achieve the above object, according to the present invention, a paper feed cassette provided with a size detection function for use in an image forming apparatus, which paper feed cassette has a rear end restricting plate for restricting the position of the rear end of paper and is removably mounted in a paper feed portion provided inside the main body of the image forming apparatus, is provided with: a plurality of detection targets arranged along the paper feed direction on the bottom of a paper stage formed integrally with the rear end restricting plate; a plurality of detection switches, arranged along the paper feed direction in the paper feed portion inside the main body of the image forming apparatus, for detecting the positions of the detection targets; and a discriminator for recognizing paper size and the presence/absence of the paper feed cassette by receiving detection signals from the detection switches. In this structure, assuming that there are provided N detection switches, it is possible to recognize at least (N+1) different paper sizes and the presence/absence of the paper feed cassette.
In this structure, the detection targets formed on the bottom of the paper stage can be formed integrally with the paper stage when it is produced. For example, in a case where the paper stage is formed out of resin, it is so molded as to have projections on the bottom thereof This eliminates the need to prepare separate members, and thus makes it possible to realize a simple and inexpensive paper feed cassette provided with a size detection function which permits the recognition of many different states of the paper feed cassette.
According to the present invention, there are provided, for example, two detection switches and four detection targets, and the discriminator permits the recognition of 3 different paper sizes and of the presence/absence of the paper feed cassette.
In this structure, on the bottom of the paper stage, four detection targets are formed at predetermined intervals along the paper feed direction, and these detection targets are detected by two detection switches arranged along the paper feed direction in the paper feed portion inside the main body of the image forming apparatus. In this way, it is possible to recognize three different paper sizes (for example, letter size, A4 size, and legal size) and whether the paper feed cassette is present or absent.